Dr James Fallon's 'professional ADHD' - as he calls it - led him to discover a pattern in the brains of psychopaths, and begin studying them.
Then he discovered he is a psychopath.
Dr Fallon is a neuroscientist at University of California, Irvine, where he studies how a number of conditions and diseases behave in the brain.
But in the 1980s, he happened to be studying the brains of killers - ones suspected to be psychopaths, using PET scans of their brains.
He also happened to decide to use scans of his family's brains as the control group for what 'normal' brains look like, and included his own.
Among the pile of family scans was one that he was sure had been placed there incorrectly. Its activity patterns were all wrong for a normal person.
But they were identical to those of a psychopath.
Dr Fallon thought someone in his lab was playing a joke. They weren't. He peeled back the piece of black tape keeping the scan anonymous - and found his own name.
Dr James Fallon is a neuroscientist who discovered brain traits that identify psychopaths, and discovered he is one in the process of his research
Only about one percent of the population are psychopaths, people who have little or no empathy or remorse.
They tend to be egotistical and lack inhibitions.
In other words, they do things like drive their kids into the African Sahara in the middle of the night without a guide to go pick up the skull of a freshly-killed crocodile, with more lurking in the water. Or steal cars in spite of an obsession with a religion that tells them 'thou shalt not steal' - and have nothing to say at Catholic Confession.
It's exhausting - it's hard to be a nice person
These are all things Dr Fallon has done, but never thought were particularly strange.
He also holds both a Master's degree and PhD, has made a number of notable scientific discoveries, has been married for many years and has raised three children.
Dr Fallon is also the type of man who will recruit his family (and himself) to act as controls in a study that might well tell them if they have early signs of Alzheimer's.
Even though his wife was 'really cool about it,' when he asked her how she felt about taking part in the study, Dr Fallon now admits 'it was kind of a mistake.'
It's also how he ended up seeing his own brain scan and recognizing all the hallmarks of psychopathy in it.
PET scans of most brains show blood flow and activity in the front orbital cortex of the prefrontal cortex (top two), but a psychopath's has very little or no blood flow (bottom)
When he saw it, Dr Fallon said to the two technicians he was working with: 'whoever this is shouldn't be walking around in society, they're a very dangerous person.'
But even then, he didn't care - a phrase he says a lot, and that gives away his true nature.
He did mention it to his wife, however.
'She said this very seriously, and I didn't realize it at the time - she's a very funny gal - she said "That doesn't surprise me,"' Dr Fallon says.
I'm not dangerous to strangers, but I tend to be a little too much fun and I get people close to me into predicaments
'There's no psychopathy genes, but there are traits associated with them, traits that drive them... I had all the genetics.'
But he 'blew it off,' he says. 'I said, "I know who am."'
It wasn't until nearly 30 years later, in 2010, when a former Norwegian prime minister and some scientists turned drinking buddies for the
